There are some excellent ideas here and I'd love to see more. Here is a quick list of five I'd like to see:

1) Overrep Bonus
Several people have mentioned a problem with the current state of Isle of Thunder dailies, namely, that players hit Exalted and stopped. This causes overall participation to drop, and slow the rate of Stage expansion. While this is a harsh example, there are other times people would want to continue doing dailies that have a rep attached, even though they are maxxed out. Think Sky Shards, for example. Or continuing to run a dungeon in BC for that Raven Never-Drop Mount over and over.

I would not mind seeing some kind of bonus for gaining rep in a faction you have at maximum. Maybe when you hit +1000 over exalted, you create a +250 rep BoA item for that same faction, and drop back to Exalted +0. Or a small amount of experience, JP or Honor depending on the faction/level. Or maybe a bag of spoils. Just a little something to make the "overrep" useful.

2) Stupid Mistake of the Tiger
I'd like Blizzard to go through their random item stat generators and remove every single useless combo from them. I admit, it probably would have very little effect on gameplay for most of us. But finding +agility plate, items which have no useful value to anyone in the game, this many years after the stats were changed, is crap. Blizzard should be ashamed for having such things, even if they are such a minor part. And hey, we've ALL worn greens at some point, haven't we?

I have personally sold Ravager Bands of the Wolf. Agility/Spirit. Nobody uses these!

3) Otra Lengua
I would like some way for characters to learn another racial language. Horde/Alliance communication will probably not happen, but a tauren who learns to speak troll makes sense. Or a DK that speaks Undercommon.

4) Deja Voodoo
I would like the ability to re-play a quest I've done before. Maybe with an ilvl reduction, as some have noted before? Maybe with the ability to purchase a different item at the end for a JP fee (500 green, 1500 blue, 3750 epic?) There are some quest/quest chains I would not mind re-doing without leveling another alt.

5) Chairman of the Board
I want a damn sandwich.

Every innkeeper from here to West Dwarven Jabip sells meat, bread, and cheese. Where are the sandwiches? I can see myself eating a Roast Beef and Fine Aged Cheddar on Mag'har Grainbread. Or a Rhino Dog with Cabbage Kim Chi (because there's no saurkraut) on a Buttery Wheat Roll, no mustard. Or Thick-Cut Bacon and more Thick-Cut Bacon on...well,anything. Food's already divided into categories because of hunter pets. We know where the bread is. This is doable!
Rule 1: Must acquire a sandwich board through N+1 Epicurean Awards.
Rule 2: Using the board brings up a UI with 3 spots for ingredients. The first must be bread, the other two anything which aren't drinks.
Rule 3: No conjured items.
Rule 4: The created sandwich gives the same health and mana as the highest of the 3 ingredients. No stats are given.
Rule 5: The created sandwich <Describes the Ingredients> in the same way as the crafter of an item.
Rule 6: Eat it. Sandwiches are awesome.

1. Proper LFR mechanic for every raid that is still playable. Queues might be long, and OpenRaid might be more efficient, but it could still work on a large scale.

2. DPS output homogenization. Utopia incarnate right here. I would like to see every DPS be within 5% of each other on aggregate, every tier. On a per fight basis numbers may vary, but they should be equal within 5% overall.

3. Complete PvP review, especially in terms of CC.

4. Reputation tabards. It might be lazy, but at least it gave the 5man dungeons a raison d'être. The daily model should award currency/loot charms/vanity items.

5. A certain amount of free character transfers/recustomizations/race changes/etc per x months. Never going to happen, for obvious reasons.

1. Tie LFR rewards to skill. Each raid boss will include three objectives that show you understand the mechanics; for each objective achieved your chance at loot will increase. This will motivate people to perform well to get better rewards and train players to be better.

2. More character customization. Add multiple new races to each side. High elves, broken, mok'nathal, forest trolls should all be playable at the very least. Add more customization to classes; e.g. let night elves choose to reskin the shadow tree to a moon tree with the exact same spells but dealing arcane (or spellfrost) damage and having arcane spell effects. I am sure we could think of other similar ideas, like troll druids using different forms than cat and bear. Always make this a choice.

3. Reconsider the heroic raiding system. Imo heroic raids should not offer an entire new ilvl of gear; make heroic raids by nature ilvl capped and add more vanity rewards to them (including updated tier looks with more spell effects), with perhaps the rare few pieces of heroic only loot that has same ilvl with normal loot but looks truly stunning. Let gear be upgraded with valor but let the weekly valor cap scale with number of heroic bosses of current tier that you have killed.

4. Allow almost all spells to be cast while moving with their casting time being extended and your speed slightly reduced. Massively reduce the number of instant heals and other instants in the game. Clearly categorize all forms of crowd control, limiting some and making DRs easier to understand to new players.

5. OK now I am overreaching Allow people to level in nearly every zone! For players that are not at max level, each zone should scale them down to a desired level and let them gain experience and level appropriate rewards by questing there. Ofc add some limit (for instance you can only get to 70 by old world zones and 85 by TBC/Wrath/Cata zones so people can't skip the last xpac of questing).

I love the 1 and 4, I think u should make a post on the official forums. I was thinking on the same lines. 3- wont happen, as the whole point of getting better is lost as the gearing up is all what is left to do at level cap.

3: Make low level content difficult again, and for the love of god add some elites whose elite status isn't completely negated by a quest item. I'd even settle for an elite who I couldn't solo without the quest item. Maybe do what they did in guild wars as well with the scaling down of high level characters, so that as a max level low level zones hold some threat.

4: Make heroic fights work the way they did in Ulduar, get rid of the stupid hit a switch, harder bosses.

1. Less focus on weekly caps; In fact, moving away from VP as a currency would be ideal. PVP might need a different solution but I feel like needing to hit an obligatory weekly cap dictates playstyle when reset is close.
--VP's intent was to help fill holes in raider's gear, thousands of other ways to achieve this that don't revolve around weekly caps.
2. Less emphasis on daily quests, or, better delivery of treadmill content.
--My problem with dailies (Repetition aside) is they don't generally have any individual weight. When you're out questing from 85 to 90, quests matter to the storyline of the zone. Dailies do not. If they made a zone, that had a full storyline which changed and reset at set intervals, that might be more immersive than a series of "Go here do these, okay you're done for today. more work tommorow"
3. More character creation/customization options. XMog is nice, but warlock's green fire scratched the surface of something bigger. Imagine being able to hit up a colorpicker and change the color of all your fire spells. Pink fire? go for it. That would enable some city of heroes esque customization.
4. On that note. New race models. Needs to happen.
5. Pre-90 Scenarios, alternatively, nerf some existing short 5-man instances to 3-man-no-tank/heals-required difficulty. would drastically improve LFG queue times while leveling.